This invention relates generally to the manufacture of angular position sensors or transducers, and, more particularly, to a novel technique for accurately center-boring angular position transducer elements.
Angular position transducers are widely used in such electro-mechanical devices as computer-controlled printers, magnetic disk drives, and video recording machines. Basically, such transducers consist of a fixed stator element and a rotatable rotor element mounted in close proximity to each other so that there is electromagnetic or electrostatic coupling between the two elements.
In one common transducer of the electromagnetic type, each element consists of a flat, circular disk, with a number of uniformly spaced, radial, conductive strips formed on an annular region of the disk, the strips being connected in series to form one continuous electrical winding. Typically, but not necessarily, the conductive strips are formed on the disk by a photo-etching process. When a carrier signal, which is usually at radio frequency, is applied to one of the elements, a similar signal is induced in the winding of the other element. More importantly, the induced signal will be amplitude-modulated, i.e., it will vary in amplitude depending on the relative angular position of the rotor and stator. The amplitude will be highest when the radial conductive strips of the two elements are aligned, and lowest when they are furthest out of alignment. Thus, as the rotor is turned, the induced signal is amplitude-modulated at a rate dependent on the angular spacing of the conductive strips. Consequently, the angular position of the rotor element may be determined to a resolution limited only by the incremental angular spacing of the strips.
It will be appreciated from the foregoing that, for the transducers to function in a highly accurate manner, it is essential that the rotor and stator elements both be mounted concentrically with the axis of rotation of the rotor. Moreover, it is preferable to eliminate any possible eccentricity during fabrication of the transducer elements, rather than depending on adjustments during installation, by ensuring that each rotor or stator element is center-bored to a high degree of accuracy. The most common method of center-boring such elements up till now has utilized an optical device to locate the center of each element. While optical methods can be extremely accurate in determining the geometric center of such an element, it is generally the case that the photo-etching or other process of depositing the conductive strips is not highly accurate, and the geometric or optical center may not, therefore, always correspond exactly with what might be termed the "electrical center" of the element.
Accordingly, it is highly desirable to locate and bore the center of each complete transducer element using electrical rather than optical methods. Although the desirability of this objective has been recognized by others in the field, there has long existed, nevertheless, a definite need for an improved, practical and convenient technique for locating and accurately boring the electrical center of a transducer element. The present invention satisfies this need.